[Crash-utility] [PATCH] Handle blk_mq_ctx member changes for kernels v5.16-rc1~75^2~44

[HAGIO KAZUHITO(萩尾 一仁)]

> -----Original Message-----
> On Fri, Dec 24, 2021 at 1:14 PM HAGIO KAZUHITO(萩尾　一仁)
> <k-hagio-ab at nec.com> wrote:
> >
> > Hi Lianbo,
> >
> > -----Original Message-----
> > > Kernel commit <9a14d6ce4135> ("block: remove debugfs blk_mq_ctx
> > > dispatched/merged/completed attributes") removed the member
> > > rq_dispatched and rq_completed from struct blk_mq_ctx. Without
> > > this patch, crash will fail with the following error:
> > >
> > > crash> dev -d
> > > MAJOR GENDISK            NAME       REQUEST_QUEUE      TOTAL ASYNC  SYNC
> > >
> > > dev: invalid structure member offset: blk_mq_ctx_rq_dispatched
> > >      FILE: dev.c  LINE: 4229  FUNCTION: get_one_mctx_diskio()
> >
> > Thank you for working on this.
> > IIUC, crash will need sbitmap functionality to support this fully.
> >
> > Meanwhile, I think it's OK to skip the count, but it should say "actually zero"
> > or "not supported" so that users can know it, for example:
> >
> Thank you for the comment, Kazu.
> 
> > crash> dev -d
> > MAJOR GENDISK            NAME       REQUEST_QUEUE      TOTAL ASYNC  SYNC
> >     8 ffff92bbd102e400   sdb        ffff92bbf04e3678       0     0     0
> > dev: sdb: Disk I/O statistics is not supported in this kernel
> >     8 ffff92bbd1014400   sdc        ffff92bbf04e26e8       0     0     0
> > dev: sdc: Disk I/O statistics is not supported in this kernel
> >    11 ffff92c347da5e00   sr0        ffff92bbd9c3e528       0     0     0
> >   253 ffff92bbca726e00   dm-0       ffff92bbcad7dd60       0     0     0
> >
> > What do you think?
> >
> 
> I agree with you that it should be good to have the above information
> for users, but it looks like the statistics result is redundant and
> the readability is not very good. What do you think of removing that
> statistical result and only outputting prompt information? For
> example:
> 
> crash> dev -d
> MAJOR GENDISK            NAME       REQUEST_QUEUE      TOTAL ASYNC  SYNC
> dev: sda: Disk I/O statistics is not supported in this kernel
> dev: sr0: Disk I/O statistics is not supported in this kernel
> dev: dm-0: Disk I/O statistics is not supported in this kernel
> dev: dm-1: Disk I/O statistics is not supported in this kernel
> dev: dm-2: Disk I/O statistics is not supported in this kernel

I would prefer to display information like the addresses of request_queue
as far as we can.  No statistics, but still we will often want to see the
structures.

So for example:

crash> dev -d
MAJOR GENDISK            NAME       REQUEST_QUEUE      TOTAL ASYNC  SYNC 
    8 ffff92bbd102e400   sdb        ffff92bbf04e3678    (not supported)
    8 ffff92bbd1014400   sdc        ffff92bbf04e26e8       0     0     0
...
crash> request_queue ffff92bbf04e3678 | head -n 3
struct request_queue {
  last_merge = 0x0,
  elevator = 0xffff92bbc449b000,

Is this possible?

Thanks,
Kazu

> 
> How about the following changes?
> ---
>  dev.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/dev.c b/dev.c
> index effe789f38d8..3cf70c41cd17 100644
> --- a/dev.c
> +++ b/dev.c
> @@ -4465,6 +4465,12 @@ display_one_diskio(struct iter *i, unsigned
> long gendisk, ulong flags)
>         if (is_skipped_disk(disk_name))
>                 return;
> 
> +       if (!MEMBER_EXISTS("blk_mq_ctx", "rq_dispatched") &&
> +               !MEMBER_EXISTS("blk_mq_ctx", "rq_completed")) {
> +               fprintf(fp, "dev: %s: Disk I/O statistics is not
> supported in this kernel\n", disk_name);
> +               return;
> +       }
> +
>         readmem(gendisk + OFFSET(gendisk_queue), KVADDR, &queue_addr,
>                 sizeof(ulong), "gen_disk.queue", FAULT_ON_ERROR);
>         readmem(gendisk + OFFSET(gendisk_major), KVADDR, &major, sizeof(int),
> --
> 
> 
> Thanks.
> Lianbo
> 
> >
> > >
> > > Signed-off-by: Lianbo Jiang <lijiang at redhat.com>
> > > ---
> > >  dev.c | 4 ++++
> > >  1 file changed, 4 insertions(+)
> > >
> > > diff --git a/dev.c b/dev.c
> > > index effe789f38d8..dd21511e5dfc 100644
> > > --- a/dev.c
> > > +++ b/dev.c
> > > @@ -4246,6 +4246,10 @@ get_mq_diskio(unsigned long q, unsigned long *mq_count)
> > >       unsigned long mctx_addr;
> > >       struct diskio tmp;
> > >
> > > +     if (!MEMBER_EXISTS("blk_mq_ctx", "rq_dispatched") &&
> > > +             !MEMBER_EXISTS("blk_mq_ctx", "rq_completed"))
> > > +             return;
> > > +
> > >       memset(&tmp, 0x00, sizeof(struct diskio));
> > >
> > >       readmem(q + OFFSET(request_queue_queue_ctx), KVADDR, &queue_ctx,
> > > --
> > > 2.20.1
> >